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This work focuses on the reconstruction of two and three dimensional images of the concentration of paramagnetic species from electron paramagnetic resonance (EPR) measurements. A direct operator, modeling how the measurements are related to the paramagnetic sample to be imaged, is derived in the continuous framework taking into account the physical phenomena at work during the acquisition process. Then, this direct operator is discretized to closely take into account the discrete nature of the measurements and provide an explicit link between them and the discrete image to be reconstructed. A variational inverse problem with total variation regularization is formulated and an efficient resolvant scheme is implemented. The setting of the reconstruction parameters is thoroughly studied and facilitated thanks to the introduction of appropriate normalization factors. Moreover, an a contrario algorithm is proposed to derive the optimal resolution at which the data should be acquired. Finally, an in-depth experimental study over real EPR datasets is done to illustrate the potential and limitations of the presented image reconstruction model.

International audience; This contribution aims to define an analysis procedure for abnormal deposits in human tissues starting from in vivo characterization, down to the nanoscale using major instrumentation. Such an integrated approach is based on recent literature, but particularly on our research over the last twenty years on pathological calcifications. To this end, we begin by describing four successive analytical steps, on the injury site or physician’s surgery, at the hospital, at a typical physicochemical laboratory, and finally at a large scale (possibly multinational) facility. For the first step, we present various techniques which can be implemented on portable instruments. For the second step, commercial analytical setups are used. In a physicochemical laboratory, prototype or commercial setups are used and finally on large scale instruments, characterization techniques with better spatial resolution and/or higher sensitivity or techniques specific to synchrotron radiation are employed.

International audience; Bispidine (3,7-diazabicyclo[3.3.1]nonane) provides a rigid and preorganized scaffold that is particularly interesting for the stable and inert complexation of metal ions, especially for their application in medical imaging. In this study, we present the synthesis of two bispidine ligands with N-methanephosphonate (H4L1) and N-methanecarboxylate (H3L2) substituents as well as the physico-chemical properties of the corresponding Mn2+ and Zn2+ complexes. The two complexes [Mn(L-1)](2- )and [Mn(L-2)](-) have relatively moderate thermodynamic stability constants according to potentiometric titration data. However, they both display an exceptional kinetic inertness, as assessed by transmetallation experiments in the presence of 50 equiv excess of Zn2+, showing only similar to 40 and 20% of dissociation for [Mn(L-1)](2- ) and [Mn(L-2)](-), respectively, after 150 days at pH 6 and 37°C. Proton relaxivities amount to r(1 )= 4.31 mM(-1 )s(-1 )([Mn(L-1)](2-)) and 3.64 mM(-1) s(-1 )([Mn(L-2)](-)) at 20 MHz, 25°C, and are remarkable for Mn2+ complexes with one inner-sphere water molecule (q = 1); they are comparable to that of the commercial contrast agent [Gd(DOTA)(H2O)](-). The presence of one inner-sphere water molecule and an associative water exchange mechanism was confirmed by temperature-dependent transverse O-17 relaxation rate measurements, which yielded k(ex)(298) = 0.12 x 10(7) and 5.5 x 10(7) s(-1 )for the water exchange rate of the phosphonate and the carboxylate complex, respectively. In addition, radiolabeling experiments with Mn-52 were also performed with H-2(L-1)(2-) showing excellent radiolabeling properties and quantitative complexation at pH 7 in 15 min at room temperature as well as excellent stability of the complex in various biological media over 24 h.

International audience; The mass and volume concentration of nanoplastics is extremely low, but incredibly high in terms of surface area; this is expected to increase their toxicity through the ab/adsorption and transport of chemical co-pollutants such as trace metals. In this context, we studied the interactions between nanoplastics model materials functionalized with carboxylated groups, with either smooth or raspberry-like surface morphologies, and copper as representative of trace metals. For this purpose, a new methodology, using two complementary surface analysis techniques: Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS) was developed. In addition, inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify the total mass of sorbed metal on the nanoplastics. This innovative analytical approach from the top surface to the core of nanoplastics demonstrated not only the interactions with copper at the surface level, but also the ability of nanoplastics to absorb metal at their core. Indeed, after 24 h of exposition, the copper concentration at the nanoplastic surface remained constant due to saturation whereas the copper concentration inside the nanoplastic keeps increasing with the time. The sorption kinetic was evaluated to increase with the density of charge of the nanoplastic and the pH. This study confirmed the ability of nanoplastics to act as metal pollutant carriers by both adsorption and absorption phenomena.

We introduce FENNIX (Force-Field-Enhanced Neural Network InteraXions), a hybrid approach between machine-learning and force-fields. We leverage state-of-the-art equivariant neural networks to predict local energy contributions and multiple atom-in-molecule properties that are then used as geometry-dependent parameters for physically-motivated energy terms which account for long-range electrostatics and dispersion. Using high-accuracy ab initio data (small organic molecules/dimers), we trained a first version of the model. Exhibiting accurate gas-phase energy predictions, FENNIX is transferable to the condensed phase. It is able to produce stable Molecular Dynamics simulations, including nuclear quantum effects, for water predicting accurate liquid properties. The extrapolating power of the hybrid physically-driven machine learning FENNIX approach is exemplified by computing: i) the solvated alanine dipeptide free energy landscape; ii) the reactive dissociation of small molecules.

Research efforts on the low temperature magnetic order and electronic properties of U$_3$O$_8$ have been inconclusive so far. Reinterpreting neutron scattering results, we use group representation theory to show that the ground state presents collinear out-of-plane magnetic moments, with antiferromagnetic coupling both in-layer and between layers. Charge localization relieves the initial geometric frustration, generating a slightly distorted honeycomb sublattice with N\'eel order. We show, furthermore, that spin-orbit coupling has a giant effect on the conduction band states and band gap value. Our results allow a reinterpretation of recent optical absorption measurements., Comment: 12 pages, including supplemental material

Uranium dioxide (UO2) is the main component of nuclear fuels. This compound is very susceptible to oxidation, which results in the formation of the mixed-valence oxide U3O8. [1] From an application point of view, this interest relates to the safe and sustainable management of nuclear fuel. Our goal is an understanding of this oxidation process at the atomic level, using ab initio electronic structure calculations. The focus of this work lies in the early oxidation of stoichiometric UO2, where excess oxygen can be treated as interstitial point defects. In order to study this oxidation we investigate the adsorption of the O atom and oxygen-containing molecules (O2, H2O, H2O2) on the three most stable UO2 surfaces ((111), (110), and (100)). The calculations are performed within DFT, using PBE+U including spin-orbit coupling and taking into account the non-collinear 3k (transverse) magnetic ground state. Dissociative adsorption is found for H2O and H2O2 on the (111) and (100) UO2 surfaces respectively, forming hydroxyl groups on the surface. Adsorption on the UO2 surface lowers the barrier for the dissociation of O2. The defect formation energy is calculated for interstitial oxygen, up to several layers into the material starting from the surface. Additionally, adsorption energies are studied as a function of temperature and partial pressure.

The process-microstructure relationship is central in materials science because the microstructure will determine the properties of the materials developed by the processes. In our work, we focused on different metallurgical processes by adopting a description at the atomic scale. This approach allows us to detect the elementary mechanisms that are at the origin of the observed microstructures without having to postulate macroscopic mechanisms or estimate the associated parameters. In this respect, molecular dynamics simulations provide a tool for "in-situ" observation of metallic systems as long as an atomic interaction potential is available. The originality of our approach consists in modeling the characteristics of the processes at nanometric scales. In the context of powder metallurgy, we focused on the additive manufacturing of metallic materials and the activation of metallic powders by high-energy milling. We performed molecular dynamics simulations to understand the directional solidification processes at the nanoscale of a pure Ni polycrystalline metal in the context of additive manufacturing. Various microstructures were observed as a function of thermal conditions. Solidification and nucleation were also compared to classical solidification and nucleation theories to establish their validity at the nanoscale. We modeled the milling process by mechanical treatment with compaction and plastic deformation to observe the action of grinding balls on a binary mixture of powders. This approach allows us to understand the behavior of mechanically activated powders (Ti+Al and Ni+Al) by characterizing atom mobility, structural transformations and reactivity. We also studied the reactivity of a Ti-Al nanometric multilayer model similar to the materials obtained after high-energy milling. We have highlighted several elementary mechanisms responsible for their increased reactivity, such as dissolution at the Ti(solid)/Al(liquid) interfaces and the formation of an intermetallic (TiAl3)., La relation procédé-microstructure est centrale en sciences des matériaux car la microstructure va déterminer les propriétés des matériaux élaborés par les procédés. Dans notre travail, nous nous sommes intéressés à différents procédés de métallurgie en adoptant une description à l'échelle atomique. Cette approche permet de déceler les mécanismes élémentaires qui sont à l'origine des microstructures observées sans avoir à postuler des mécanismes macroscopiques et estimer les paramètres associés. A cet égard, les simulations par dynamique moléculaire fournissent un outil d'observation "in-situ" des systèmes métalliques pour autant qu'un potentiel d'interaction atomique soit disponible. L'originalité de notre démarche a été de modéliser les caractéristiques des procédés aux échelles nanométriques. Dans le contexte de la métallurgie des poudres, nous nous sommes intéressés à la fabrication additive de matériaux métalliques et à l'activation des poudres métalliques par broyage à haute énergie. Nous avons réalisé des simulations de dynamique moléculaire afin de comprendre les processus de solidification directionnelle à l'échelle nanométrique d'un métal polycristallin de Ni pur dans le contexte de la fabrication additive. Différentes microstructures ont été observées en fonction des conditions thermiques. La solidification et la nucléation ont également été comparées aux théories classiques de la solidification et de la nucléation afin d'en établir la validité aux échelles nanométriques. Nous avons modélisé le procédé de broyage par un traitement mécanique sous la forme d'une compaction et d'une déformation plastique pour rendre compte de l'action des billes de broyage sur un mélange binaire de poudres. Cette approche permet de comprendre le comportement des poudres activées mécaniquement (Ti+Al et Ni+Al) en caractérisant la mobilité des atomes, les transformations structurelles et la réactivité. Nous avons également étudié la réactivité d'un modèle multicouche nanométrique Ti-Al similaire aux matériaux obtenus après un broyage très énergétique. Nous avons mis en évidence plusieurs mécanismes élémentaires responsables de leur réactivité exacerbée comme la dissolution aux interfaces Ti(solide)/Al(liquide) et la formation d'intermétallique (TiAl3).

International audience; Starch represents one of the primary products of photosynthesis in the chloroplast and plays the role of storage polysaccharide in most green algae and plants. The green alga Chlamydomonas reinhardtii has been used for years as a microbial model to explore the intricate pathway of starch synthesis in the green lineage. This chapter emphasizes the use of Chlamydomonas to probe functions involved in starch synthesis, degradation and granule morphology. In addition, particular attention is given to the evolution of the green lineage specific complexity of starch metabolism, explaining the basic similarities and differences between green algae and land plants as well as between the latter and the red algae and glaucophytes. Applied aspects and future prospects are discussed.

International audience; This article describes the synthesis, spectroscopic studies, and theoretical calculations of nine original fluorophores based on the 2-(2′-hydroxyphenyl)benzazole (HBX) scaffold, functionalized at the 4-position of the phenol ring by ethynyl-extended aniline moieties. HBX dyes are well-known to display an excited-state intramolecular proton transfer (ESIPT) process, owing to a strong six-membered hydrogen bond in their structure that allows for an enol/keto tautomerism after photoexcitation. Appropriate electronic substitution can perturb the ESIPT process, leading to dual fluorescence, both excited tautomers emitting at specific wavelengths. In the examples described herein, it is demonstrated that the proton transfer can be finely frustrated by a modification of the constitutive heteroring, leading to a single emission band from the excited enol or keto tautomer or a dual emission with relative intensities highly dependent on the environment. Moreover, the nature of the functionalization of the N-alkylated aniline moiety also has a significant importance on the relative excited-state stabilities of the two tautomers in solution. To shed more light on these features, quantum chemical calculations by the density functional theory are used to determine the excited-state energies and rationalize the experimental spectroscopic data.

International audience; The significant advances in synthesis and functionalization have enabled the preparation of high-quality nanoparticles that have found a plethora of successful applications. The unique physicochemical properties of nanoparticles can be manipulated through the control of size, shape, composition, and surface chemistry, but their technological application possibilities can be further expanded by exploiting the properties that emerge from their assembly. The ability to control the assembly of nanoparticles not only is required for many real technological applications, but allows the combination of the intrinsic properties of nanoparticles and opens the way to the exploitation of their complex interplay, giving access to collective properties. Significant advances and knowledge gained over the past few decades on nanoparticle assembly have made it possible to implement a growing number of strategies for reversible assembly of nanoparticles. In addition to being of interest for basic studies, such advances further broaden the range of applications and the possibility of developing innovative devices using nanoparticles. This review focuses on the reversible assembly of nanoparticles and includes the theoretical aspects related to the concept of reversibility, an up-to-date assessment of the experimental approaches applied to this field and the advanced computational schemes that offer key insights into the assembly mechanisms. We aim to provide readers with a comprehensive guide to address the challenges in assembling reversible nanoparticles and promote their applications.

The burning of fossil fuels is the major culprit of greenhouse gases emission contributing to the global climate crisis. Among many alternative energy solutions, the nuclear power stands out for its capacity in massive production. However, the intense nuclear reactions create a detrimental environment for reactor materials. To understand the material damages caused by radiations, experiments traditionally use neutron beams. These experimental settings are often expensive with samples difficult to manipulate. These disadvantages are the reasons why the use of ion beams becomes a popular alternative. One key parameter for the ion irradiation is the electronic stopping power, whose value is usually obtained from the SRIM code. This empirical method is based on a very complete database. However, it may lose its reliability when the irradiated systems have hardly any experimental records in the database. Calculations from first-principles thus provide supplementary references to experiments. Implemented inside the MOLGW code, our simulation method for the electronic stopping power is based on the time-dependent density functional theory (TDDFT). Using localized Gaussian-type orbital basis functions, our code can describe all the electrons, core and valence. The main goal of this thesis is to incorporate basis functions following the movement of the projectile and simulate the irradiation of ions containing electrons. Modifications to the time-dependent equations, notably the appearance of an operator D, are necessary due to the movement of projectile basis. This extra operator enforces the conservation of the wave-function orthonormality and has an amount of energy contribution whose numerical precision depends on the basis set completeness. The Crank-Nicolson propagator is chosen over the second-order Magnus propagator due to less approximations required in the non-orthogonal basis. A predictor-corrector scheme is applied to evaluate the propagated states. In order to reduce the computational costs of large matrix updates during the propagation, only the cross target-projectile elements are selected for recalculations. The sanity of our implementations is verified by tests in atomic systems before applying the code to solid targets. Since our approach works with finite systems, the infinite crystal structure is represented by a cluster. Two main groups of modeling parameters vital to the convergence are studied: the cluster geometry and the basis set quality. We advocate for the use of a long and thin cylindrical shape for the clusters to guarantee the stabilization of the energy transfer between the projectile and the target. High quality cc-pVXZ Dunning basis are needed for target atoms and projectiles with core electrons. For lighter projectiles the standard cc-pVXZ basis is sufficient. The channeling stopping powers of hydrogen and helium are studied in fcc [001] aluminum target and converge faster when the cluster is centered on its channel rather than on its central column of atoms. The random electronic stopping powers of hydrogen and helium in lithium and aluminum are presented, as well as the results for aluminum ion in aluminum. Our calculations, although not fully converged, provide accurate qualitative insights of the stopping power behaviors in good general agreement with the SRIM prediction, the experimental data and the results obtained with plane-wave basis method from another group. We also report the random stopping powers of proton and antiproton in LiF calculated without projectile basis from a side project. Our results describe correctly the proton stopping power observed by experiments like the threshold velocity and the Barkas effect where the stopping power of antiproton is inferior to that of proton. Additionally, we have observed an unprecedented negative Barkas effect at very low velocities due to the destabilization of the 2p orbitals of F⁻ ions in the presence of a close antiproton., La consommation de combustibles fossiles est un facteur principal des émissions de gaz à effet de serre. Face à une crise climatique planétaire, des solutions énergétiques alternatives s'imposent. L'énergie nucléaire présente l'avantage de la production de masse, mais expose les matériaux de structure à un environnement extrême dont les dommages doivent être étudiés. Les expériences traditionnelles utilisant des faisceaux de neutrons sont souvent coûteuses avec des échantillons difficiles à manipuler. Une meilleure alternative est l’irradiation aux ions. Une quantité importante mesurée lors de l’irradiation aux ions est le pouvoir d’arrêt, dont la référence la plus standard est le SRIM. Cette méthode empirique de calculs est ajustée sur une base de données expérimentales très complète. Mais pour les irradiations peu documentées, la fiabilité du SRIM n'est pas garantie et les calculs ab initio peuvent servir de références supplémentaires. Implémentée au sein du code MOLGW, notre méthode de simulation s'appuie sur la théorie de la fonctionnelle de la densité dépendante du temps (TDDFT). L'utilisation de fonctions de base localisées du type gaussienne permet de décrire tous les électrons. L'objectif de cette thèse est d'introduire des fonctions de bases localisées suivant le projectile pour prendre en compte de ses électrons. Puisque la base du projectile se déplace, les équations de Schrödinger dépendantes du temps doivent être modifiées. On constate notamment l’apparition d’un opérateur D indispensable à la conservation d’orthonormalité de fonction d’onde. Cet opérateur contribue à une quantité d'énergie dont la précision numérique dépend fortement de la qualité de base. Le propagateur de Crank-Nicolson est choisi à la place du propagateur de Magnus du second ordre, en raison du fait que ce premier nécessite moins d'approximations dans une base nonorthogonale. Une stratégie de prédiction-correction est appliquée à la propagation. La mise à jour de matrices de grande taille demande beaucoup d'efforts de calcul pendant la propagation. Afin de réduire le coût, seuls les termes croisés entre la cible et le projectile sont sélectionnés pour le recalcul. L'implémentation a été validée par des tests de collisions atomiques avant d'être appliquée aux cibles solides. Notre approche traite les systèmes finis et les structures cristallines sont décrits par les agrégats. Deux groupes de paramètres de modélisation sont vérifiés par rapport à la convergence : la géométrie de l’agrégat et la qualité de base. On conseille un agrégat de forme cylindrique fin et long pour assurer la stationnarité du transfert d'énergie. Quant à la base, les séries cc-pVXZ de Dunning sont les plus adaptées pour les atomes de cible ainsi que pour les projectiles possédant d’électrons de coeur. Pour les projectiles plus légers, les séries standard cc-pVXZ suffisent. Les pouvoirs d’arrêt canalisés le long des directions cristallines (channeling en anglais) d’hydrogène et d’hélium sont étudiés dans un agrégat d’aluminium fcc [001]. Les résultats du channeling convergent plus rapidement quand l'agrégat est centré sur le canal. Les pouvoirs d’arrêt moyennés (random en anglais) d’hydrogène et d’hélium dans le lithium et l’aluminium sont analysés, ainsi que celui d’aluminium dans l’aluminium. Malgré un léger manque de convergence, nos résultats sont qualitativement corrects et en bon accord avec le SRIM, les données expérimentales et les résultats obtenu en base d'ondes planes par un autre groupe. Enfin une étude en parallèle de pouvoirs d’arrêt de proton et d’antiproton dans le LiF calculés sans la base de projectile sont montrés. Nos simulations décrivent correctement les comportements du pouvoir d’arrêt de proton observés par les expériences. En outre, on prédit un effet de Barkas négatif sans précédent à très basse vitesse. On explique cet effet par la déstabilisation d’une orbitale 2p d’ion F⁻ par un antiproton proche.

International audience; Frozen Density Embedding (FDE)[1,2] represents a versatile embedding scheme which allows to model complex molecular systems by partitioning the total system into sub-units: the environmental effects onto a given subsystem is described by accounting quantum mechanically for the surrounding subsystems through their electron density.The accurate modeling of properties of matter when heavy elements are involved requires the inclusion of relativistic corrections. The Dirac-Kohn-Sham (DKS) method allows one to treat electron correlation and relativistic effects on the same footing.The response of electrons in atoms and molecules to an applied external electro-magnetic field can be efficiently treated employing Time-Dependent Density Functional Theory (TDDFT) in the real-time domain (RT-TDDFT)[3].We extend the full 4-component relativistic RT-TDDKS[4] method, as implemented in the BERTHA code, to include environmental and confinement effects with the FDE scheme (RT-TDDKS-in-DFT FDE)[5].Moreover, we demonstrate that the implementation of rather complex numerical algorithms can be enormously facilitated by BERTHA’s python API (PyBERTHA) which, besides all the well-known Python advantages, eases the interoperability with other FDE implementations available through the PyADF framework.References:1. Wesolowski, T. A.; Warshel, A. Frozen density functional approach for ab initio calculations of solvated molecules. J. Chem. Phys. 1993, 97, 8050–8053. 2. Höfener, S.; Gomes, A. S. P.; Visscher, L. Molecular properties via a subsystem density functional theory formulation: a common framework for electronic embedding. J. Chem Phys, 2012, 136(4), 044104.3. Lopata, K.; Govind, N. Modeling Fast Electron Dynamics with Real-Time Time-Dependent Density Functional Theory: Application to Small Molecules and Chromophores. J. Chem. Theory Comput. 2011, 7, 1344–13554. De Santis, M.; Storchi, L.; Belpassi, L.; Quiney, H. M.; Tarantelli, F. PyBERTHART: A Relativistic Real-Time Four-Component TDDFT Implementation Using Prototyping Techniques Based on Python. J. Chem. Theory Comput. 2020, 16, 2410–2429. 5. De Santis, M.; Sorbelli, D.; Vallet, V.; Gomes, A. S. P.; Storchi, L.; Belpassi, L. Frozen-Density Embedding for including environmental effects in the Dirac-Kohn-Sham theory: an implementation based on density fitting and prototyping techniques. https://doi.org/10.48550/arXiv.2205.05523

National audience; The O(N6) computation cost is a bottleneck preventing performing Coupled-Cluster (CC) on large systems, particularly when employing 4- component based relativistic Hamiltonians, for which in practice one often uses uncontracted basis set generating large virtual molecular orbitalspaces.The canonical Hartree-Fock (HF) orbitals are not the most compact representation for post HF method. On other hand, using natural orbital is an efficient way to reduce the orbital space and maintains most of the accuracy. We therefore implemented the MP2 frozen natural orbital (FNO) method [1] in the Exacorr code [2], with the particularity that our implementation can generate both complex and quaternion FNOs, and also express these in AO basis. It also allows us to obtain CCSD natural orbitals on AO basis, which can be subsequently used in analysis. We have investigated the orbital truncation errors in both correlation energy and molecular properties including dipole, quadrupole moment, electric filed gradient, for hydrogen halides HX (X=F, Cl, Br, I, At, Ts), and parity violation for the H2X2 (X= O, S, Se, Te, Po) molecules. We find that FNO indeed accelerates rapidly the correlation energy convergence. For properties, truncated FNO spaces seem to slightly outperform canonical HF orbitals, and to provide reliable estimates for the molecular properties obtained for complete virtual spaces [3].Reference[1] T. L. Barr, E. R. Davidson, Phys. Rev. A 1970, 1, 644; A. G. Taube, R. J. Bartlett, J. Chem. Phys. 2008, 128, 164101[2] J. V. Pototschnig, A. Papadopoulos, D. I. Lyakh, M. Repisky, L. Halbert, A. S. P. Gomes, H- JAa. Jensen, L. Visscher, J. Chem. Theory. Comput. 2021, 17, 5509[3] X. Yuan, L. Visscher, ASP. Gomes, J. Chem. Phys. 2022, arXiv:2202.01146

International audience; Uranyl complexes have been the subject of many research works for fundamental chemistry of actinides, environmental issues, or nuclear fuel cycle processes. The formation of various uranyl complexes, with organic and inorganic ligands in solution must be characterized for a better understanding of U(VI) speciation. As uranyl-ligand interactions and the symmetry of the complexes affect the electronic structure of U(VI) and thus its luminescence properties, time-resolved laser induced fluorescence spectroscopy (TRLFS) is one of the major techniques to characterize U(VI) complexes, with high sensitivity and selectivity. However, most of the relevant systems have complex chemical composition in solution and the identification of each species from spectroscopic data is challenging.In our study, the synergy between TRLFS and ab initio-based interpretation appears as a promising route for complexation data. Luminescence spectra of uranyl complexes in solution show in general a narrow energetical range about 6000 cm-1 and we can identify a single electronic transition between the initial and target states with the vibrationally resolved band [1]. The main challenge consists in exploiting a computationally cheap and effective theoretical approach, in a relativistic context, to characterize the main spectral parameters of the ground and luminescent states of symmetrical uranyl compounds (i.e. UO2Cl42-, UO2F53-, UO2(CO3)34-, UO2(NO3)L2) with different organic or inorganic counter ions after the photo-excitation. We will illustrate that TD-DFT with the CAM-B3LYP functional is able to provide accurate excitation/emission energies for these systems, together with accurate vibronic progressions allowing the assignment of experimental data.As a benchmark system serving the purpose of assessing the accuracy of our theoretical protocol, the uranyl tetrachloride UO2Cl42- was selected because of the extensive amount of structural and spectroscopic data available [2]. A good agreement was found between ours and previously obtained theoretical data (structural parameters, orbitals nature, excitation energies) [3]; the final luminescence spectrum is in remarkable agreement with our TRLFS measurements [4]. We will also quantify the effects of organic or inorganic counterions [5, 6], along with that of first-sphere ligands that might perturb the uranyl(VI) moiety.This work showcases how one can predict vibrationally resolved spectra to assign the recorded TRLFS data, and shed light on the relationship between the uranyl coordination and its luminescence properties.[1] J. Visnak et al. (2006) EPJ Web Conf. 128, 02002.[2] R.G. Denning et al. (1991) Chem. Phys. Lett. 180, 101.[3] K. Pierloot et al. (2005) J. Chem. Phys. 123, 204309.[4] H. Oher et al. (2020) Inorg. Chem. 59, 5896.[5] H. Oher et al. (2020) Inorg. Chem. 59, 15036.[6] H. Oher et al. (2022) Inorg. Chem. 61, 890.

International audience; Accurate electronic structure calculations have become an indispensable tool to understand the molecular properties of heavy and superheavy elements. Such approaches help make sense of the underlying complex physical processes probed by experiments, or in the case such experiments are unfeasible due to the heavy elements’ radiotoxicity.In this presentation I will outline our contributions to developments of coupled cluster approaches based on four-component Hamiltonians for ground-state properties as well as for valence and core excitation and ionization spectra [1-4], and their application to investigating heavy and super heavy elements [2, 3, 5].Furthermore, I will outline how these can be combined with more approximate approaches through embedding theories [6], to enable the investigation of heavy element species in complex environments such as in solution.Funding: ANR-11-LABX-0005-01, ANR-19-CE29-0019, ANR-16-IDEX-0004, DE-AC05- 00OR22725.References[1] J. Pototschnig et al., J. Chem. Theory Comput. (2021) 17, 5509 10.1021/acs.jctc.1c00260 [2] X. Yuan, L. Visscher, A. S. P. Gomes, J. Chem. Phys. (in press) (2022). 10.1063/5.0087243[3] A. Shee, T. Saue, L. Visscher, A. S. P. Gomes, J. Chem. Phys. (2018) 149, 174113 10.1063/1.5053846[4] L. Halbert, M. L. Vidal, A. Shee, S. Coriani, A. S. P. Gomes, J. Chem. Theory Comput. (2021) 17, 3583 10.1021/acs.jctc.0c01203[5] S. Kervazo, F. Réal, F. Virot, A. S. P. Gomes, V. Vallet, Inorg. Chem. (2019) 58, 14507 10.1021/acs.inorgchem.9b02096[6] Y. Bouchafra, A. Shee, F. Réal, V. Vallet, A. S. P. Gomes, Phys. Rev. Lett. (2018) 121, 266001 10.1103/PhysRevLett.121.266001

National audience

International audience; The role of short chain branches (SCBs) (C4H9) on the melt and crystalline properties of monodisperse polyethylene systems (C400H802) is investigated, using molecular dynamics simulations of a coarse-grained united-monomer model that represents a chemical monomer as one particle. A method is introduced, whereby SCBs are grown out of the linear backbone to minimize computational expense. Here, this concept is proven by introducing differing numbers (Nb = 0, 1, 2, 4, 10, and 20) of regularly spaced SCBs along the chain backbones and studying their influence on the melt and crystalline properties. By growing SCBs into the melt phase, it is demonstrated that they marginally perturb the original topology, justifying a relatively short equilibration time after growth. Upon crystallization, however, each system’s behavior differs considerably. Cooling and heating cycles are performed to study crystallization and melting at progressively slower rates. The crystalline morphology is observed to depend strongly on both cooling rate and number of branches along the linear backbone. In particular, the lamella thickness decreases systematically with both faster cooling and increasing SCB content. At the highest branch content, of one per 20 backbone carbons (Nb = 20), crystallization is almost entirely suppressed, whereas a small number of branches allows control over the average lamellar thickness. This observation, combined with a prudent method for equilibrating systems with SCBs, opens up opportunities to study more complex chain architectures and mimic industrial polyethylene morphologies.

International audience; Intrinsically disordered proteins (IDPs) or intrinsically disordered regions (IDRs) is a class of biologically important proteins exhibiting specific biophysical characteristics. They lack a hydrophobic core, and their conformational behavior is strongly influenced by electrostatic interactions. IDPs and IDRs are highly dynamic, and a characterization of the motions of IDPs and IDRs is essential for their physically correct description. NMR together with molecular dynamics simulations are the methods best suited to such a task because they provide information about dynamics of proteins with atomistic resolution. Here, we present a study of motions of a disordered C-terminal domain of the delta subunit of RNA polymerase from Bacillus subtilis. Positively and negatively charged residues in the studied domain form transient electrostatic contacts critical for the biological function. Our study is focused on investigation of ps-ns dynamics of backbone of the delta subunit based on analysis of amide 15N NMR relaxation data and molecular dynamics simulations. In order to extend an informational content of NMR data to lower frequencies, which are more sensitive to slower motions, we combined standard (high-field) NMR relaxation experiments with high-resolution relaxometry. Altogether, we collected data reporting the relaxation at 12 different magnetic fields, resulting in an unprecedented data set. Our results document that the analysis of such data provides a consistent description of dynamics and confirms the validity of so far used protocols of the analysis of dynamics of IDPs also for a partially folded protein. In addition, the potential to access detailed description of motions at the timescale of tens of ns with the help of relaxometry data is discussed. Interestingly, in our case, it appears to be mostly relevant for a region involved in the formation of temporary contacts within the disordered region, which was previously proven to be biologically important.

In this paper, we present a variational treatment of the linear dependence for a non-orthogonal time-dependent basis set in solving the Schrödinger equation. The method is based on (i) the definition of a linearly independent working space and (ii) a variational construction of the propagator over finite time steps. The second point allows the method to properly account for changes in the dimensionality of the working space along the time evolution. In particular, the time evolution is represented by a semi-unitary transformation. Tests are carried out on a quartic double-well potential with Gaussian basis functions whose centers evolve according to classical equations of motion. We show that the resulting dynamics converges to the exact one and is unitary by construction.

International audience; The incorporation of actinides in lanthanide phosphate matrices crystallizing in the monazite structure has been intensely investigated in the past decades due to the relevance of these monazites as potential ceramic host phases for the immobilization of specific high level radioactive waste (HLW) streams [1-3]. In recent years, understanding the incorporation behaviour of trivalent dopants in the LnPO4•xH2O rhabdophane structure has been given more attention [4,5]. Rhabdophane is the hydrated phosphate precursor in the synthesis of monazites through precipitation routes and a potential secondary mineral controlling actinide solubility in dissolution and re-precipitation reactions of monazite host-phases. Despite the large interest in lanthanide phosphates and the interaction of actinides with these solids, very little data [6-8] is available on the complexation of lanthanides and actinides with aqueous phosphates, even though these complexation reactions precede any aqueous synthesis of monazite ceramics and are expected to occur in natural waters as well as in the proximity of monazite-containing HLW repositories. In many cases, an independent spectroscopic validation of the stoichiometry of the proposed complexes, is also missing. Both from the perspective of aqueous rhabdophane synthesis, which is often carried out at elevated temperatures, and heat-generating HLW immobilization in monazites, the lanthanide and actinide complexation reactions with aqueous phosphates under ambient conditions should be complemented with data obtained at higher temperatures.In the present work, laser-induced luminescence spectroscopy was used to study the complexation of Cm(III) (1.15×10-8 to 1.15×10-7 M) as a function of total phosphate concentration (0 to 0.08 M) in the temperature regime 25-90 °C, using NaClO4 as a background electrolyte (I = 0.5 to 3.0 M). These studies have been conducted in the acidic pH-range (−log10 [H+] = 1.00, 2.52, 3.44, and 3.65) to avoid precipitation of solid Cm rhabdophane. For the first time, in addition to the presence of CmH2PO42+ already evidenced before [6,7], the formation of Cm(H2PO4)2+ was unambiguously established from the luminescence spectroscopic data collected at the various H+ concentrations previously mentioned [8].The conditional complexation constants of both aqueous complexes were found to increase upon rising ionic strength and temperature. Extrapolation of the obtained complexation constants to infinite dilution at 25 °C was performed by applying the Specific Ion Interaction Theory (SIT) [9]. The obtained log10 β° values for CmH2PO42+ and Cm(H2PO4)2+ were 0.45 ± 0.04 and 0.08 ± 0.07 [8], respectively, for reactions 1 and 2 below:Cm3+ + H3PO4 ⇌ CmH2PO42+ + H+ (1)Cm3+ + 2 H3PO4 ⇌ Cm(H2PO4)2+ + 2 H+ (2)The ion interaction coefficients ε(CmH2PO42+;ClO4-) = 0.17 ± 0.04 and ε(Cm(H2PO4)2+;ClO4-) = −0.10 ± 0.06 were derived at 25 °C [8]. Temperature-dependent conditional complexation constants for the identified species were obtained from the recorded luminescence emission spectra. They were subsequently extrapolated to I =0 M, assuming that the ion interaction parameters obtained at 25 °C are not significantly impacted by the temperature increase from 25 °C to 90 °C [6]. Using the integrated van´t Hoff equation, both the molar enthalpy of reaction ΔrHm° and entropy of reaction ΔrSm° values were found to be positive for the two complexes, namely CmH2PO42+ and Cm(H2PO4)2+ [8].Relativistic quantum chemical investigations revealed a monodentate binding of the H2PO4- ligand to the central Cm3+ ion to be the most stable configuration for both complexes. By combining ab initio calculations with a thorough analysis of the obtained luminescence spectroscopic data, both CmH2PO42+ and Cm(H2PO4)2+ complexes with an overall CN of 9 were shown to be stable in solution at 25 °C. However, a different temperature-dependent evolution of the coordination of the Cm3+ ion to hydration water molecules could be derived from the electronic structure of the Cm(III)-phosphate complexes. More specifically, an overall coordination number of 9 was retained for the CmH2PO42+ complex in the investigated temperature range (25 to 90 °C), while a coordination change from 9 to 8 was established for the Cm(H2PO4)2+ species with increasing temperature [8]. This change of coordination upon increasing temperature, which has not been investigated in detail in the past, might also be relevant in the complexation of other f-elements with inorganic and/or organic ligands and deserves further exploration.[1] R. C. Ewing, Proc. Natl. Acad. Sci. USA 96, 3432 (1999).[2] D. Bregiroux et al., J. Nucl. Mater. 366, 52 (2007).[3] N. Huittinen et al., J. Nucl. Mater. 486, 148 (2017). [4] E. Du Fou de Kerdaniel, J. Nucl. Mater. 362, 451 (2007).[5] N. Huittinen et al., Inorg. Chem. 57, 6252−6265 (2018).[6] H. Moll et al., Radiochim. Acta, 99, 775−782 (2011).[7] N. Jordan et al., Inorg. Chem. 57, 7015-7024 (2018).[8] N. Huittinen et al., Inorg. Chem. 60, 10656−10673 (2021).[9] I. Grenthe et al., Second update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technetium, OECD Nuclear Energy Agency Data Bank, Eds., OECD Publications, Paris, France, (2020).

Photoreduction of perylenediimide (PDI) derivatives has been widely studied for use in photocatalysis, hydrogen evolution, photo-responsive gels, and organic semiconductors. Upon light irradiation, the radical anion (PDI⋅- ) can readily be obtained, whereas further reduction to the dianion (PDI2- ) is rare. Here we show that full 2-electron photoreduction can be achieved using UVC light: 1) in anaerobic conditions by 'direct photoreduction' of PDI aggregates, or 2) by 'indirect photoreduction' in aerobic conditions due to acetone ketyl radicals. The latter strategy is also efficient for other dyes, such as naphthalenediimide (NDI) and methylviologen (MV2+ ). Efficient photoreduction on the minute time-scale using simple LED light in aerobic conditions is attractive for use in dissipative light-driven systems and materials.

The considerable attention paid to metal halide perovskites (MHP) in recent years led to several scientific and technological advances, among which the creation of a new photovoltaic (PV) technology that competes with the most widespread ones[1]. With the ever-increasing diversity of applications explored, the need for fundamental understanding persists and may be gained either by smart and simple experimental protocols or models, or else via complex set-ups and computationally expensive ab-initio calculations.At present, MHP materials used in devices are frequently far from their ideal bulk structure, which hinders the use of state-of-the-art first principles simulations including many-body effects and calls for the design of dedicated models. For PV and LEDs, they are mixed with each other in complex alloys and heterostructures, including 2D/3D compositions, combined with additives or protecting layers to improve their stability and/or defectiveness as well as assembled with carrier selective layers. On the other hand, colloidal MHP nanocrystals are promising for devices exploiting both weak and strong light-matter interactions, such as lasers, single photon emitters if not all-optical logic gates. After a general introduction on MHPs, the talk will bring up some of the hot topics in the field and will summarize recent results obtained by the group in Rennes in collaboration with our partners from France and abroad[2-6]. References : [1] https://www.nrel.gov/pv/cell-efficiency.html and https://www.nrel.gov/pv/module-efficiency.html.[2] W. Li et al., Light-activated interlayer contraction in two-dimensional perovskites for high-efficiency solar cells, Nature Nanotechnology, 17, 45 (2022)[3] B. Traore et al., A theoretical framework for microscopic surface and interface dipoles, work functions and valence band alignments in 2D and 3D halide perovskite heterostructures, ACS Energy Lett. 7, 349 (2022) [4] B. Traore et al., Band gap and energy level alignment of 2D and 3D halide perovskites using DFT-1/2, Phys. Rev. Materials, 6, 014604 (2022)[5] S. Sidhik et al., Deterministic fabrication of 3D|2D 1 perovskite bilayer 2 stacks for durable and efficient solar cells, accepted. [6] Q. Akkerman, et al., Taming the nucleation and growth kinetics of lead halide perovskite quantum dots, https://doi.org/10.21203/rs.3.rs-1236393/v1

International audience; Biofuels and other biomass-derived chemicals are now considered as a vital part of sustainable energy portfolio, where they promise to contribute to our society’s energy security. Despite the undeniable interest presented by these biofuels, their combustion processes are likely to modify the formation of PAHs and OPAHs that may profoundly modify the properties of formed soot particles. In this work, five laminar premixed flames of anisole (a surrogate for lignin-based biofuels) and hydrocarbon fuel blends have been investigated using advanced gas chromatography which is equipped with a pre-concentration device to trap sufficient material in order to allow detection of PAHs and OPAHs at ppb levels. Employing this sample enrichment technique has enabled us to spot around 100 aromatic species in chromatographic analysis. Besides PAHs, several oxygenated aromatics (phenol, cresols, benzofurans, xanthones, etc.) were detected which highlights their significant co-formation. Moreover, anisole addition in flames is found to increase the formation of polyaromatic compounds. These species would allow us to link several primary reactions with the formation of pollutants and potential soot particles formed during the combustion of biofuels. The present results build a solid database for analysing OPAH/PAH co-formation during the combustion of lignin-based biofuels. Moreover, the impact of the biofuel composition on soot formation is envisioned to be studied in this project.

International audience; Zinc ions (Zn 2+) play an important biological role in many diseases, hence an imaging method for monitoring the Zn 2+ distribution in tissues could provide important clinical insights. Recently, we reported a potent Zn-sensitive probe based on the Gd-DO3A (DO3A-1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylic acid), modified tyrosine and DPA (di-(2-picolyl)amine) chelator for this metal cation, which generates outstanding magnetic resonance imaging (MRI) response. Here we further explored the origin of this unprecedented response and expanded the choice of the potential MRI probes by preparing the free acid version of the initial MRI sensor. We report a detailed investigation of the 1 H nuclear magnetic relaxation dispersion (NMRD), 17 O NMR and isothermal titration calorimetry properties of these two MRI probes upon interacting with Zn 2+. The performed experiments confirm the selective interaction of the MRI probes and the target metal cation, which causes substantial changes in the coordination sphere of the paramagnetic center. It also evidenced some aggregation which enhances the relaxivity response. Interestingly, conversion of the methyl ester to the free carboxylic acid of tyrosine moiety changes the nature of the aggregates and leads to a smaller relaxivity response. The probes interact with human serum albumin (HSA) in the absence of Zn 2+ , which leads to a possible modification of the coordination sphere of Gd 3+ or a substantial change in the exchange rate of second sphere water molecules. In the presence of Zn 2+ , the interaction with HSA is very weak, demonstrating the importance of the Zn 2+ coordination sphere in the behavior of these systems.

International audience; Enantiomeric excesses of l-amino acids have been detected in meteorites; however, their molecular mechanism and prebiotic syntheses are still a matter of debate. To elucidate the origin of homochirality, alanine and the chiral precursors formed in prebiotic processes were investigated with regard to their stabilities among their isomers by employing the minimum energy principle, namely, the abundancy of a molecule in the interstellar medium is directly correlated to the stability among isomers. To facilitate the search for possible isomers, we developed a new isomer search algorithm, the random connection method, and performed a thorough search for all the stable isomers within a given chemical formula. We found that alanine and most of its precursors are located at higher energy by more than 5.7 kcal mol−1, with respect to the most stable isomer that consists of a linear-chain structure, whereas only the 2-aminopropanenitrile is the most stable isomer among all others possible. The inherent stability of the α-amino nitrile suggests that the 2-aminopropanenitrile is the dominant contribution in the formation of the common enantiomeric excess over α-amino acids.

International audience

International audience

International audience; While the generation of aryl radicals by photoredox catalysis is well-documented under reductive conditions, it has remained challenging under an oxidative pathway. Because of the easy photooxidation of alkyl bis-catecholato silicates, a general study on phenyl silicates bearing substituted catecholate ligands has been achieved. The newly synthesized phenyl silicates have been fully characterized and their reactivity has been explored. It was found that thanks to the substitution of the catecholate moiety and notably with the 4-cyanocatecholato ligand, the phenyl radical could be generated and trapped. Computational studies provided a rationale for these findings.

International audience; Persistent luminescence and photochromism are two fascinating optical properties that involve charge trapping via defects and their release due to an external stimulation. In both processes, it is possible to define 1 (or on) and 0 (or off) optical states. Consequently, materials with one of these phenomena find major interest in view of designing smart, anticounterfeiting, and optical information storage devices. Combining both processes within a single material can lead to a new generation of information storage phosphors, in which it may be possible to obtain three different optical states by playing on the external stimulations applied on the material. For that purpose, the elaboration of nickel-doped ZnGa2O4 spinet transparent nano-glassceramics is presented in this work. The short-wave infrared (SWIR) emission, a broad band located at ca. 1275 nm, arises from Ni2+ cations located in gallium octahedral sites. SWIR persistent luminescence, arising from the same doping ion transition, can also be monitored after UV charging. Interestingly, UV irradiation not only leads to persistent luminescence charging but also to a reversible photochromism effect. By means of a complete optical characterization study combined with electron paramagnetic resonance measurements, the origins of both the persistent luminescence emission and the photochromism are explored. Finally, a discussion on the advantages of such a material combining both persistent luminescence and photochromism properties, leading to three possible optical states of the material, is dressed in view of possible optical memory systems.

International audience

International audience; Homogeneous nucleation, which plays an important role in cloud and dust particle formation, consists of a succession of unions of small gas-phase molecules leading to the formation and growth of droplets and particles. At high degrees of supersaturation the rate-limiting step of nucleation is the complexation of the two smallest molecular species involved, known as dimerisation. We have employed an adaptation ofthe Chirped Pulse in Uniform Flow (CPUF) technique to study the gas phase kinetics of complexation processes. This technique employs the CRESU (reaction kinetics in uniform supersonic flow) method coupled with chirped-pulse Fourier transform millimetre-wave spectroscopy, combining the capability of generating continuous cold uniform supersonic flows at high degrees of supersaturation with the high selectivity and general applicability of rotational spectroscopy. We have studied the complexation kinetics of a number of different molecules including acrylonitrile and formic acid, and our latest results will be presented.

International audience; Uranyl complexes have been the subject of many research works for fundamental chemistry of actinides, environmen-tal issues, or nuclear fuel cycle processes. The formation of various uranyl complexes, with organic and inorganic ligands in solution must be characterized for a better understanding of U(VI) speciation. As uranyl-ligand interactions and the symmetry of the complexes affect the electronic structure of U(VI) and thus its luminescence properties, time-resolved laser induced fluorescence spectroscopy (TRLFS) is one of the major techniques to characterize U(VI) com-plexes, with high sensitivity and selectivity. However, most of the relevant systems have complex chemical composi-tion in solution and the identification of each species from spectroscopic data is challenging.In our study, the synergy between TRLFS and ab initio-based interpretation appears as a promising route for com-plexation data. Luminescence spectra of uranyl complexes in solution show in general a narrow energetical range about 6000 cm-1 and we can identify a single electronic transition between the initial and target states with the vibrationally resolved band [1]. The main challenge consists in exploiting a computationally cheap and effective theoretical ap-proach, in a relativistic context, to characterize the main spectral parameters of the ground and luminescent states of symmetrical uranyl compounds (i.e. UO2Cl42-, UO2F53-, UO2(CO3)34-, UO2(NO3)L2) with different organic or inorganic counter ions after the photo-excitation. We will illustrate that TD-DFT with the CAM-B3LYP functional is able to provide accurate excitation/emission energies for these systems, together with accurate vibronic progressions allowing the assignment of experimental data.As a benchmark system serving the purpose of assessing the accuracy of our theoretical protocol, the uranyl tetrachloride UO2Cl42- was selected because of the extensive amount of structural and spectroscopic data available [2]. A good agreement was found between ours and previously obtained theoretical data (structural parameters, orbitals nature, excitation energies) [3]; the final luminescence spectrum is in remarkable agreement with our TRLFS measurements [4]. We will also quantify the effects of organic or inorganic counterions [5, 6], along with that of first-sphere ligands that might perturb the uranyl(VI) moiety.This work showcases how one can predict vibrationally resolved spectra to assign the recorded TRLFS data, and shed light on the relationship between the uranyl coordination and its luminescence properties.

The high computational scaling with the number of correlated electrons and the size of the basis set is a bottleneck which limits applications of coupled cluster (CC) algorithms. This is particularly so for calculations based on 2- or 4-component relativistic Hamiltonians, which often employ uncontracted basis sets and lead to large virtual molecular orbital (VMO) spaces. This problem may be alleviated by employing a more compact set of virtual spinors than those provided by the canonical Hartree-Fock (HF) set, such as those based on natural orbitals (NOs). In this paper we describe the implementation of a module for generating NOs for correlated wavefunctions, and in particular MP2 frozen natural orbitals (MP2FNOs), as a component of our novel implementation of relativistic coupled cluster theory for massively parallel architectures [J. Pototschnig et. al., J. Chem. Theory Comput. 17, 5509, 2021]. Our implementation is capable of manipulating both complex and quaternion density matrices, thus allowing for the generation of both Kramers-restricted and Kramers-unrestricted MP2FNOs. Furthermore, NOs are re-expressed in the parent atomic orbital (AO) basis, so that the code also makes it possible to generate CCSD natural orbitals in AO basis for further analysis. By investigating the truncation errors of MP2FNOs for both the correlation energy and molecular properties at CCSD level such as the electric field gradients at the nuclei (EFGs), electric dipole and quadrupole moments for hydrogen halides HX (X=F-Ts), and parity-violating energy differences (PV) for H$_2$Y$_2$ (Y=O-Se), we find that MP2FNOs accelerate the convergence of the correlation energy in a roughly uniform manner across the periodic table and that, with VMO spaces truncated to around half the size of the full spaces ones, it is possible to obtain reliable estimates for both energies and all molecular properties considered., Comment: 16 pages, 9 figures

International audience

The first chapter of this thesis will provide a brief overview of the diversity of photobases. The different families of photobases will be discussed, with an emphasis on the mechanisms involved in their photolysis.The 2nd chapter will focus on a study of the photophysical and photochemical properties of the photobase under study in order to map and quantify these phenomena (such as fluorescence, or triplet excited states). The third chapter will describe an original method for calculating the generated base quantum yields via the use of a stationary spectroscopic technique. Photobase yields will be evaluated in different media. The 4th chapter will aim to put the results of the previous chapter into perspective with the use of a nanosecond transient spectroscopic technique. In addition, the efficiency of the base release reaction will be correlated with the photophysical properties of the solvents in which the photobase can be found. The 5th chapter will focus on the finalisation of this photochemical pathway, with the quantification of certain rate constants via the use of a femtosecond transient spectroscopic technique. And finally the 6th chapter will attempt to determine the rate of production of the base released during photolysis of the photobase., Le 1er chapitre de cette thèse constituera un bref aperçu de la diversité des photobases. Les différentes familles de ces dernières seront abordées, avec un accent sur les mécanismes mis en jeux lors de leur photolyse. Le 2ème chapitre portera sur une étude des propriétés photophysiques et photochimiques de la photobase d’étude afin de cartographier et quantifier ces phénomènes (tel que la fluorescence, ou les états excité triplets). Le 3ème chapitre décrira une méthode originale de calcul de rendement quantique en base généré via l’utilisation d’une technique spectroscopique stationnaire. Les rendements de la photobase seront évalués dans différents milieux. Le 4ème chapitre aura pour but de mettre en perspective les résultats du précédent chapitre avec l’utilisation d’une technique spectroscopique transitoire nanoseconde. De plus, l’efficacité de la réaction de libération de la base sera mise en corrélation avec les propriétés photophysiques des solvants dans lesquels la photobase peut se trouver. Le 5ème chapitre portera sur la finalisation de cette route photochimique, avec la quantification de certaines constantes de vitesse via l’utilisation d’une technique spectroscopique transitoire femtoseconde. Et enfin le 6ème chapitre tentera de déterminer la vitesse de production de la base libérée lors de la photolyse de la photobase.

International audience

Nuclear magnetic resonance (NMR) spin relaxation experi-ments currently probe molecular motions on timescales from picoseconds to nanoseconds. The detailed interpretation of these motions in atomic detail benefits from complementarity with the results from molecular dynamics (MD) simulations. In this mini-review, we describe the recent developments in experimental techniques to study the backbone dynamics from 15N relaxation and side-chain dynamics from 13C relaxation, discuss the different analysis approaches from model-free to dynamics detectors, and highlight the many ways that NMR relaxation experiments and MD simulations can be used together to improve the interpretation and gain insights into protein dynamics. ISSN:0959-440X ISSN:1879-033X

International audience; Small molecules targeting the PD-1/PD-L1 checkpoint are actively searched to complement the anticancer arsenal. Different molecular scaffolds have been reported, including phenyl-pyrazolone derivatives which potently inhibit binding of PD-L1 to PD-1. These molecules are structurally close to antioxidant drug edaravone (EDA) used to treat amyotrophic lateral sclerosis. For this reason, we investigated the capacity of five PD-L1-binding phenyl-pyrazolone compounds (1–5) to scavenge the formation of oxygen free radicals using electron spin resonance spectroscopy with DPPH/DMPO probes. In addition, the reactivity of the compounds toward the oxidized base 5-formyluracil (5fU) was assessed using chromatography coupled to mass spectrometry and photodiode array detectors. The data revealed that the phenyl-pyrazolone derivatives display antioxidant properties and exhibit a variable reactivity toward 5fU. Compound 2 with a N-dichlorophenyl-pyrazolone moiety cumulates the three properties, being a potent PD-L1 binder, a robust antioxidant and an aldehyde-reactive compound. On the opposite, the adamantane derivative 5 is a potent PD-L1 binding with a reduced antioxidant potential and no aldehyde reactivity. The nature of the substituent on the phenyl-pyrazolone core modulates the antioxidant capacity and reactivity toward aromatic aldehydes. The molecular signature of the compound can be adapted at will, to confer additional properties to these PD-L1 binders.

International audience

Organic semiconductor materials such as planar conjugated small molecules are of great interest to the photovoltaic community. In thin films, the exciton and charge carrier dynamics, which are crucial to photovoltaic device operation, depend in a non-trivial way on the organic molecular structure and on the molecular organization in the solid state. Recently, the exciton diffusion has been found to strongly depend on the crystalline order of the organic thin films. This work presents the study of the exciton lifetime in an innovative class of molecular semiconductors able to present different crystalline order. This family of molecules has a “dumbbell-shaped” structure based on triazatruxene units that act as a π-stacking platform. Such molecules with different side-chains have been found to self-assemble into various crystalline and liquid crystalline phases. We have studied the steady-state photoluminescence and the exciton lifetime for several triazatruxene-based derivatives with different side-chains, in solution and in thin films for different solid state phases. In solution, the fluorescence lifetime corresponds to the reference value that can be obtained without intermolecular interaction. In thin films, we measured the exciton lifetime for different molecular structures in order to correlate the exciton dynamics with the molecular stacking. The results reveal a significant increase in the exciton lifetime with the enhancement of the structural order.

International audience; The stability constants of Mn2+ complexes with ligands containing a trans-1,2-cyclobutanediamine spacer functionalized with picolinate and/or carboxylate functions were determined using potentiometric titrations (25 °C, 0.1 M KCl). The stability constant of the complex with a hexadentate ligand containing four acetate groups (L14−, log KMnL = 10.26) is improved upon replacing one (L24−, log KMnL = 14.71) or two (L34−, log KMnL = 15.81) carboxylate groups with picolinates. The [Mn(L1)]2− complex contains a water molecule coordinated to the metal ion in aqueous solutions, as evidenced by 1H NMRD studies and 17O chemical shifts and transverse relaxation rates. The 1H relaxivities determined at 60 MHz (3.3 and 2.4 mM−1 s−1 at 25 and 37 °C, respectively) are comparable to those of monohydrated complexes such as [Mn(edta)]2−. The exchange rate of the inner-sphere water molecule (k298ex = 248 × 106 s−1) is slightly lower than that of the edta4− analogue. DFT calculations (M11/def2-TZVP) suggest that the water exchange reaction follows a dissociatively activated mechanism, providing activation parameters in reasonably good agreement with the experimental data. DFT calculations also show that the 17O hyperfine coupling constant A/ℏ is affected slightly by changes in the Mn–Owater distance and the orientation of the water molecule with respect to the Mn–O vector.

International audience; In order to introduce students to the fascinating field of femtochemistry, we propose here a practical laboratory training course conceived for second-year master's students in chemistry. We describe the use of a broadband femtosecond transient absorption (pump−probe) experiment for monitoring a fast light-triggered chemical reaction in solution. The experiments are performed on the pyranine photoacid, which upon photo-excitation at 390 nm undergoes a proton transfer to the solvent in about 90 ps. While this practical course involves advanced equipment and techniques, the measured transient absorption data allow easy analysis and interpretation. The transient absorption spectra at a few selected delay times can be analyzed qualitatively in terms of bleach, induced absorption, and stimulated emission. Likewise, the transient absorption signals at a few chosen wavelengths can be quantitatively analyzed and explained with simple kinetic models to determine the time constant of the proton-transfer reaction. This training aims at giving the students the opportunity to face some of the current challenges in contemporary chemistry by learning the basics of ultrafast spectroscopy.

From corrosion layers to high-performance storage devices, the Fe-Cr-O ternary system contains typical “old” materials with widespread applications. In this PhD thesis, the macroscopic behavior of this multifaceted system is analyzed in the light of their microscopic properties. To do so, a comprehensive investigation of high-purity, epitaxial Fe-Cr-O thin films is performed in combination with theoretical calculations. Focus is placed on two stable structures of the Fe-Cr-O system: ∝-Cr₂O₃ and (Fe,Cr)₃O₄ series. The first part of this thesis holds a discussion about the effects of lattice strain in the electronic structure of ∝-Cr₂O₃ thin films. Here epitaxial ∝-Cr₂O₃(0001) thin films were synthetized in three model strain scenarios: completely relaxed, under compressive or under tensile in-plane strain. For each scenario, Cr 2p X-ray photoemission (XPS) spectra were recorded and their features were analyzed by crystal field multiplet (CFM) calculations. According to this approach, the lattice strains introduce distortions in the Cr local environment that split the 3d valence orbitals triplet t2g into a1 + e orbitals. For relaxed thin films, the XPS spectroscopic signatures were well reproduced by CFM calculations when the t2g subset was fully degenerated. Meanwhile, spectra of films under tensile (or compression) in-plane strain were simulated properly when a1 orbitals was stabilized (or destabilized) with respect to e orbitals. Therefore, one proved that subtle changes observed in the lines-shape of the Cr 2p XPS spectrum can be used to identify stress states on complex oxides. This convenient methodology (XPS+CFM), which was first optimized using model samples, was then used to successfully identify stress states on polycrystalline ∝-Cr₂O₃ layers grown during the oxidation of a commercial chromia-forming alloy. The second part of this thesis holds a discussion about the effects of composition, cation disorder and microstructure on the physical properties of (Fe,Cr)₃O₄ thin films. Here stoichiometric series of epitaxial (Fe,Cr)₃O₄(111) thin films were prepared by molecular beam epitaxy (MBE) and their structural, chemical and physical properties were studied by a number of characterization methods. These thin films are composed by Cr³⁺ ions sitting exclusively at octahedral (Oh) interstices and Fe²⁺ and Fe³⁺ ions distributed at Oh and tetrahedral (Td) interstices of the spinel structure. Once again, spectroscopic signatures (here from X-ray magnetic circular dichroism or XMCD) of Cr and Fe were explored by CFM calculations in order to obtain their valence and local environment. More importantly, we were able to determine the cation site distribution, i.e. the relative concentration of each specie on each interstice of the spinel structure. This information is crucial in the analysis of physical properties. In general, we observed that increasing Cr content steadily decreases the magnetic moment and increases the resistivity of the (Fe,Cr)₃O₄ thin films, which is consistent with previous studies in bulk samples. However, unlike bulk structures, the thin films kept an intermediate spinel structure (i.e. Fe²⁺ and Fe³⁺ ions in both Oh and Td-sites) for high Cr content. Because of that, all thin films presented Curie temperatures (Tc) above the room temperature, which is further proved using another theoretical model: the atomistic spin simulations. Furthermore, three possible conductive paths (involving electron hopping between Fe²⁺ and Fe³⁺ sites) were analyzed for the (Fe,Cr)₃O₄( thin films. Because both Fe²⁺ and Fe³⁺ ions sit at Oh-sites (even at high Cr content), these films are less resistive than the bulk as the favored Oh-to-Oh electron-hopping path is still available. In conclusion, we showed that tuning the physical properties of the (Fe,Cr)₃O₄ series can be achieved through the composition and size modulation., Les spinelles fer – chrome et la chromine sont des composés du système ternaire Fe-Cr-O qui sont présents aussi bien dans les couches de corrosion des aciers inoxydables que dans les dispositifs de stockage haute performance. L’enjeu de cette thèse est de lier des observations à l’échelle microscopique (par exemple, la structure électronique ou l’occupation des sites cationiques) à des grandeurs physiques macroscopiques (par exemple, la résistivité ou l’aimantation) sur ces matériaux sous forme de couches minces « modèle » épitaxiées. L’utilisation ciblée de calculs théoriques a permis d’apporter une interprétation fine de certaines mesures expérimentales. La première partie de la thèse est dédiée à l’étude de l’effet de la déformation de films minces de chromine ∝-Cr₂O₃ sur ses propriétés électroniques. Les couches minces de chromine ∝-Cr₂O₃(0001) sont d’abord synthétisées par jets moléculaires (MBE) suivant trois états de contrainte : tension, compression dans le plan ou parfaitement relaxé. Pour chaque cas, les spectres des niveaux 2p du chrome ont été mesurés par photoémission de rayons X (XPS) et analysés à l’aide de calculs de multiplets (méthode CFM). Les résultats montrent que les distorsions de l’environnement local du chrome, lié à la déformation, lèvent la dégénérescence du triplet t2g des orbitales 3d en une orbitale et deux orbitales dégénérées a1 + e. On remarque ainsi que la signature XPS de la chromine complètement relaxée correspond à une dégénérescence des orbitales t2g. La tension (ou compression) dans le plan induit quant-à-elle une stabilisation (ou déstabilisation) de l’orbitale a1 par rapport aux orbitales e. L’analyse des spectres XPS des niveaux 2p du chrome apparaît dès lors être un outil pour identifier l’état de contrainte de la chromine. Au-delà du cas des couches minces épitaxiées utilisées pour mettre au point la démarche, il a été ensuite possible de suivre l’évolution de l’état de contrainte de la couche de ∝-Cr₂O₃ polycrystalline obtenue durant l’oxydation in situ d’un alliage commercial nickel-chrome. La seconde partie de cette thèse est consacrée aux effets de composition, de désordre et de microstructure sur les propriétés physiques de films minces de spinelles (Fe,Cr)₃O₄. A nouveau, la première étape a consisté à synthétiser par MBE des films minces épitaxiés de (Fe,Cr)₃O₄(111) de haute qualité structurale et chimique. L’analyse des mesures obtenues par dichroisme magnétique circulaire (XMCD) à l’aide de calculs CFM a permis d’extraire l’environnement local (i.e. valence et occupation des sites cationiques) du fer et du chrome dans ces spinelles, en fonction de la teneur en chrome. Les résultats montrent (i) que le chrome est dans l’état Cr³⁺ et se substitue au fer en position octaédrique (Oh) exclusivement, (ii) que les cations Fe²⁺ et Fe³⁺ sont redistribués dans les deux sites tétraédrique (Td) et octaédrique (Oh) et (iii) que l’évolution du taux d’inversion dans les films est plus faible que pour les composés massifs à mesure que la concentration en chrome augmente. La quantification de cette redistribution s’est révélée cruciale pour interpréter les mesures macroscopiques. Ainsi, il a été possible de relier l’évolution de l’aimantation en fonction de la concentration en chrome au taux d’inversion. De plus, l’augmentation de la résistivité avec la teneur en chrome a pu être associée à la disponibilité des chemins de sauts d’électrons Oh–Oh, c’est-à-dire à la concentration en fer dans les sites octaédriques.

International audience; The considerable attention paid to metal halide perovskites (MHP) in recent years led to several scientific and technological advances. This in turn raised important questions that currently challenge the limits of available theoretical techniques and atomistic models. At present, perovskite materials are mixed with each other in complex alloys and heterostructures, including 2D/3D compositions, combined with additives or protecting layers to improve their stability and/or defectiveness as well as assembled with carrier selective layers, other materials and components to turn them into devices. Considering the target applications, ambient conditions predominate with additional issues related, for example, to the intrinsic dynamics in action in the MHP structure that may not be well captured using static averaged structures.Based on a set of customized examples, this talk will summarize recent theoretical results obtained by our group that aimed at answering questions such as: i) How do these engineering strategies impact the work function and absolute valence band energy of the MHP material? ii) Is it correlated with surface/interface dipoles? iii) Can one quantitatively assess energy level alignments of MHP semiconductors based on first-principles electronic structure calculations? How can one get rid of the stochastic dynamics of organic cations and further include cation and anion alloying while computing materials properties? iv) Is it possible to extract semi-empirical formula for molecular passivation at surface or transitivity rules for interface dipoles? Special attention will be paid on newly discovered phases and compositions and opportunities to further engineer MHP properties in connection with their use in devices under working conditions.*This research received funding from the European Union’s Horizon 2020 program, through and Innovation Action under the grant agreement No. 861985 (PeroCUBE). J.E. acknowledges the Institut Universitaire de France.

International audience; The activation of rhodopsin, the light-sensitive G-protein-coupled receptor responsible for dim-light vision in vertebrates, is driven by an ultrafast excited-state double-bond isomerization with a quantum efficiency of almost 70%. The origin of such light sensitivity is not understood and a key question is whether in-phase nuclear motion controls the quantum efficiency value. In this study we used hundreds of quantum-classical trajectories to show that, 15 fs after light absorption, a degeneracy between the reactive excited state and a neighbouring state causes the splitting of the rhodopsin population into subpopulations. These subpopulations propagate with different velocities and lead to distinct contributions to the quantum efficiency. We also show here that such splitting is modulated by protein electrostatics, thus linking amino acid sequence variations to quantum efficiency modulation. Finally, we discuss how such a linkage that in principle could be exploited to achieve higher quantum efficiencies would simultaneously increase the receptor thermal noise leading to a trade-off that may have played a role in rhodopsin evolution.

International audience; Incorporating many-body and environment effects on core and luminescence propertiesMatteo De Santis, Hanna Oher, Florent Réal, André Severo Pereira Gomes, Valérie ValletUniv. Lille, CNRS, UMR 8523 - PhLAM - Physique des Lasers Atomes et Molécules, F-59000 Lille, FranceX-ray photoelectron spectrometry (XPS), X-ray absorption spectroscopy (XAS) and luminescence time-resolved laser induced fluorescence spectroscopy (TRLFS) are all spectroscopic techniques that can probe the coordination and local environment around a given complex. The first part of the talk will be devoted to the interpretation of luminescence spectra of uranium(VI), since its speciation is a key challenge in the context of the nuclear fuel cycle. Owing to its high sensitivity and selectivity time-resolved laser induced fluorescence spectroscopy (TRLFS) is particularly suited for such studies. However, most of the relevant systems have complex chemical composition in solution and the identification of each species from spectroscopic data is challenging. We will detail our efforts in developing an ab initio-based interpretation of TRLFS data. We will illustrate that TD-DFT with the CAM-B3LYP functional is able to remedy the flaws that plagued previous applications of DFT in the determination of vertical excitation and emission energies for these systems. We will illustrate how one can predict vibrationally resolved spectra useful it is to assign the recorded TRLFS data [1, 2, 3].The second part of this presentation will focus on core spectra of hydrated halides, owing to their relevance to atmospheric chemistry. We resort to quantum chemical methods in the framework of quantum embedding approaches [4] since these, at the same time, allow for the halogen can in principle be treated at a sufficiently high level of theory (to account, for example, for both correlation and relaxation effects [5] due to the creation of the core hole), while still retaining a quantum description for the whole system (so that we can obtain information from, or couplings to, the environment) and achieving an overall reduction of computational effort. We will present the recent implementation (in the non-relativistic framework) and carry out a first assessment of the performance of two quantum embedding approaches, frozen density embedding (FDE) and the block-orthogonalized Manby-Miller embedding (BOMME), for the calculation of XAS for model systems, employing real-time time-dependent density functional theory (rt-TDDFT) [6].[1] H. Oher, F. Réal, T. Vercouter, V. Vallet, Inorg. Chem. 59, 5896 (2020).[2] H. Oher, T. Vercouter, F. Réal, C. Shang, P. E. Reiller, V. Vallet, Inorg. Chem. 59, 15036 (2020).[3] H. Oher, G. Ferru, L. Couston, L. Berthon, D. Guillaumont, F. Réal, T. Vercouter, V Vallet, ChemRxiv (2021), 10.33774/chemrxiv-2021-9sjjh, preprint.[4] A. S. P. Gomes and C. R. Jacob, Annu. Rep. Prog. Chem., Sect. C: Phys. Chem. 108, 222 (2012).[5] L. Halbert, M.L. Vidal, A. Shee, S. Coriani, A.S.P. Gomes, J. Chem. Theory Comput. 17, 3583 (2021) [6] M. De Santis, V. Vallet, A.S.P. Gomes, https://arxiv.org/abs/2111.13947

International audience; The O(N6) high computational cost is a bottleneck preventing performing Coupled-Cluster (CC) on large systems, particularly when employing 4-component based relativistic Hamiltonians, for which in practice one often uses uncontracted basis set generating large virtual molecular orbital (VMO) spaces. The canonical Hartree-Fock (HF) orbitals are not the most compact representation for post HF method. Alternative, using natural orbitals is an efficient way to reduce the orbital space while retaining accuracy. We therefore implemented the MP2 frozen natural orbital (FNO) method [1] in the Exacorr code [2], with the particularity that our implementation can generate both complex and quaternion FNOs, and also express these in AO basis. It also allows us to obtain CCSD natural orbitals on AO basis, which can be subsequently used in analysis. We have investigated the orbital truncation errors for both correlation energy (at CCSD(T) level) and molecular properties (at CCSD level) such as the electric field gradients at the nuclei (EFGs ), dipole and quadrupole moments for hydrogen halides HX (X=F, Cl, Br, I, At, Ts), and parity violation energy shift for the H2X2 systems (X= O, S, Se, Te, Po). We find that using FNOs accelerates the convergence of the correlation energy in a roughly uniform manner across the periodic table and that, with VMO spaces truncated to around half of the complete ones, we obtain reliable estimates for both energies and molecular properties in the complete VMO spaces.[1] T. L. Barr, E. R. Davidson, Phys. Rev. A 1970, 1, 644; A. G. Taube, R. J. Bartlett, J. Chem. Phys. 2008, 128, 164101[2] J. V. Pototschnig, A. Papadopoulos, D. I. Lyakh, M. Repisky, L. Halbert, A. S. P. Gomes, H- J Aa. Jensen, L. Visscher, J. Chem. Theory. Comput. 2021, 17, 5509

Ultrafast electron diffraction is a powerful technique that can resolve molecular structures with femtosecond and angstrom resolutions. We demonstrate theoretically how it can be used to monitor conical intersection dynamics in molecules. Specific contributions to the signal are identified which vanish in the absence of vibronic coherence and offer a direct window into conical intersection paths. A special focus is on hybrid scattering from nuclei and electrons, a process that is unique to electron (rather than X-ray) diffraction and monitors the strongly coupled nuclear and electronic motions in the vicinity of conical intersections. An application is made to the cis to trans isomerization of azobenzene, computed with exact quantum dynamics wavepacket propagation in a reactive two-dimensional nuclear space.